1. Field of the Invention
The present invention relates to a machine tool having a spindle which has a tool receptacle for an interchangeable tool holder which is chucked into the tool receptacle during operation of the machine tool and which has a coolant tube for receiving a cooling lubricant, furthermore having a first passage which is arranged in the interior of the spindle and has an outlet opening which opens out inside the tool receptacle, the coolant tube, when a tool holder is chucked, engaging in the outlet opening of the first passage.
The invention also relates to a tool holder for such a machine tool, having an external taper for being chucked into a tool receptacle of the machine tool and having a coolant tube for receiving a cooling lubricant.
2. Related Prior Art
Such a machine tool and a corresponding tool holder are known, for example, from DE 197 26 942 A1.
The known machine tool has a spindle which is rotatably mounted in a spindle housing and on the end face of which a receptacle for the tool holder is provided centrally. The tool holders are standardized as a rule. So-called HSK tool holders, which have a hollow shank taper for being clamped into the tool receptacle, are becoming more common. In this case, the tool receptacle has a chucking system with collets which engage in the interior of the hollow shank taper in order to chuck the tool holder in a rotationally fixed manner. The collets are normally actuated via a collet spigot which is provided on the end of a chucking rod arranged axially in the spindle.
In the known machine tool, an inner passage runs through the spindle in the axial direction. The inner passage opens out with an outlet opening centrally at the base of the tool receptacle, the bottom end of the inner passage being formed by a bore through which the chucking rod passes. A coolant tube of the chucked tool holder engages in the outlet opening formed in this way. This provides a continuous passage through which a cooling lubricant can be directed from a coolant source via the spindle and the tool holder to the tool. The cooling lubricant used in the known machine tool is an oil-water emulsion (CL).
A special aspect in the known machine tool is that the cooling lubricant does not just serve to cool and lubricate the tool during the machining of a workpiece. This is because, during a tool change, when the entire tool holder plus the tool is exchanged as a rule, the cooling lubricant also serves here to clean the tool holder, in particular its external tapered and plane surfaces, of chips and any other dirt particles. To this end, the tool holder is rinsed with the cooling lubricant at least when approaching the tool receptacle.
The known machine tool therefore only needs a single inner passage, which serves to cool and lubricate the tool and also to clean the tool holder. This permits an especially simple and thus cost-effective construction.
In addition to the use of a cooling fluid for cooling and lubricating a tool, it is in principle also known to use “minimum quantity lubrication”. In this case, an aerosol, preferably in the form of an oil/air mixture, is used instead of the cooling fluid. As the name already implies, the quantity of cooling lubricant required in the case of minimum quantity lubrication is considerably smaller than when using a cooling fluid.
Now it is desirable to operate a machine tool of the type described above with the simplest possible means, even with minimum quantity lubrication. When putting this into practice, however, it has been found that it is difficult to ensure a continuous and uniform flow of the cooling lubricant. Further investigations have shown that one cause of this is cavities, edges and other irregularities of the inner passage of the known machine tool, in particular in transition and coupling regions. At high speeds of the spindle, the oil from the aerosol collects at such locations and sinks. If the speed of the spindle is reduced or the spindle is braked, for example for a tool change, the oil flows off from the sinking locations, which leads to an increased quantity of oil at the outlet opening of the inner passage. If the spindle is then accelerated again to high speeds, first of all some of the oil supplied in the aerosol collects at the sinking locations. Consequently, the quantity of oil provided at the outlet opening of the inner passage may at first be too small after a tool change. Under unfavourable conditions, there is the risk of the tool and/or of the machined workpiece being damaged as a result.
DE 84 30 433 U1 discloses a machine tool which has a twin-passage system. To cool the tool during the machining of a workpiece, a cooling lubricant is fed via an axially arranged first inner passage. In this known machine tool, however, the inner passage for the cooling lubricant opens out outside the locating space for the tool holder. To clean the tool holder during a tool change, a second inner passage via which compressed air is supplied during the tool change is provided in this known machine tool. The second inner passage opens out centrally at the base of the locating space for the tool holder.
The tool holders of this known machine tool have no coolant tube of the type described above, via which a cooling lubricant is directed to the tool. On the contrary, the document attaches importance to the fact that precisely no cooling lubricant passes into the region of the tool receptacle. In addition, this known machine tool is also not intended for minimum quantity lubrication.